THE DEPENDENCE OF OCEAN BACKSCATTER AT K-U-BAND ON OCEANIC AND ATMOSPHERIC PARAMETERS

The Jet propulsion Laboratory NUSCAT K-u-band scatterometer successful ly acquired ocean backscatter data over a wide variety of oceanic and atmospheric conditions during the Surface Wave Dynamics Experiment (SW ADE), Ten flights resulted in 30 h of data collection were conducted o n the NASA Ames C130 aircraft, The SWADE experimental area was deploye d with several buoys providing appropriate in situ measurements to cor relate with the radar backscatter for incidence angles from 10 to 60 d egrees at both horizontal and vertical polarizations, The NUSCAT-SWADE backscatter data base was utilized in conjunction with buoy measureme nts to investigate ocean backscatter signatures over the range of cond itions encountered during SWADE, To account for modulations and fluctu ations in incidence angles, a backscatter analysis independent of a pr iori geophysical model functions was developed, tested, and implemente d, Results for backscatter azimuth modulations in terms of upwind, dow nwind, and crosswind radar returns are compared to airborne RADSCAT re sults and to SASS-I and II geophysical model functions versus neutral wind speed (U-N). NUSCAT-SWADE results are closest overall to SASS-II values, fit best with SASS-I at 10 degrees incidence angle, and are si gnificantly higher than RADSCAT, Effects of friction velocity (u), wa ve age (c(0)/u), and significant wave height (H-1/3) on ocean backsca tter are studied, The backscatter shows a good positive sensitivity to u, an inverse dependence on c(0)/u*, and no systematic trend with H- 1/3 excluding cases of large swells, Coefficients of empirical relatio ns between backscatter and neutral wind speed, friction velocity, and wave age are derived for 10-40 degrees incidence angles at both horizo ntal and vertical polarizations, Covariance studies of backscatter wit h the derived relations to winds show an overall deviation factor in t he order of 1 dB for ocean signatures including uncertainties in surfa ce conditions.